From an environmental concern standpoint, especially a carbon dioxide (CO2) reduction standpoint, a dual-fuel engine has been developed, which can switch fuel between liquid fuel such as gasoline and a gas fuel such as hydrogen gas.
One example of such a dual-fuel engine is described in JP2007-162632.
In this reference, a control method for a dual-fuel engine in which the type of applied fuel is changed by a driver between gasoline (liquid fuel) and hydrogen gas (gas fuel) is described. Specifically, when an amount of evaporated fuel trapped in a canister meets a predetermined condition such that a canister purge should be implemented, an air-fuel ratio of hydrogen gas provided into an engine is set to a leaner value than a stoichiometric ratio, and then the purge is implemented, which results in decreasing the torque increase that can be generated by a canister purge operation.
According to the methods described in this reference, because the operating mode is not changed forcibly from a hydrogen using mode to a gasoline using mode when the canister purge is implemented, torque fluctuations that accompany canister purge operations may be reduced, further, a torque increase of the engine due to the canister purge operation may be offset by a leaner air-fuel ratio.
Another example of a dual-fuel engine is described in JP2008-88864. In this reference, a control method for a dual-fuel engine in which applied fuel is changed by a driver between gasoline (liquid fuel) and hydrogen gas (gas fuel) is described. Specifically, a dual-fuel engine is described that uses hydrogen gas as a fuel when a catalyst provided in an exhaust system of the engine is not activated to have sufficient performance, as long as a remaining amount of hydrogen gas is not below a predetermined value. And after the catalyst is activated, when the predetermined condition is met, fuel switching is restricted such that gasoline is forcibly used as a fuel.
According to the method described in this reference, exhaust emission quality can be improved while the catalyst is not yet activated and hydrogen gas fuel that is required when the catalyst is not activated can be saved, by restricting usage of hydrogen gas fuel while using gasoline fuel positively after the catalyst is activated.
By using gas fuel with no carbon until the catalyst is activated during cold engine start as described in reference of JP2008-88864, emission quality can be improved in comparison with using hydrocarbon fuel.
However, the inventors herein have recognized that because there are various patterns depending on engine operating conditions and/or environmental factors for generating evaporated fuel in a gasoline tank, it is difficult to inhibit generation of evaporated fuel itself even if the driver can select fuel provided in an engine.
Even if a driver is environment-oriented and selects a gas fuel, when providing evaporated fuel, a so-called canister purge is implemented while the catalyst is not activated, and as a result, dissociation and purification of hydrocarbon may be implemented insufficiently, and therefore, non-purified exhaust gas would be undesirably exhausted into the atmosphere.
Especially, in the case that a driver selects a gas fuel, lean combustion with lean air-fuel ratio mostly occurs, and a temperature of exhaust gas may be below 300 degrees C. during lean operation with low crankshaft revolution speeds. In this case, the quantity of heat inputted into the catalyst becomes increasingly smaller, and therefore, there is a greater tendency to increase unpurified hydrocarbon.
The present description is made considering the above described issue and addresses a simultaneous pursuit of providing evaporated fuel during cold engine conditions and improvement of exhaust gas purification performance.
A first aspect of the present description includes a method for controlling a dual-fuel engine that has an evaporated gas providing device for providing an evaporated gas into the engine and is operable with non-hydrocarbon fuel or hydrocarbon fuel, alternatively, the method comprising: operating said engine with one of the fuels on the basis of a driver's request; in response to the determination of a cold engine operation, operating said engine with non-hydrocarbon fuel for a specified period irrespective of a driver's request; determining that an evaporated fuel is to be provided into said engine; and if it is determined that the evaporated fuel is to be provided into said engine when the engine is operating with non-hydrocarbon fuel due to the determination of the cold engine conditions, then switching to operation with hydrocarbon fuel and thereafter providing evaporated fuel into the engine.
This method overcomes at least some of the disadvantages of the above related art.
Specifically, this control method operates the engine with non-hydrocarbon fuel for a specific period irrespective of a driver's request during cold operation. Further, in the case that providing evaporated fuel is requested during operation with non-hydrocarbon fuel, by switching to hydrocarbon fuel operation before providing the evaporated fuel, heat is provided to the catalyst.
Thus, by operating the engine with non-hydrocarbon fuel for a specific period irrespective of a driver's request during the cold engine conditions, an amount of exhaust gas requiring purification is reduced or minimized.
Further, when providing evaporated fuel is requested, by operating the engine with hydrocarbon fuel having higher heat value, it becomes possible to operate the engine with a minimum amount of hydrocarbon fuel and to restrict generation of hydrocarbons due to providing evaporated fuel.
In one embodiment, the method may further comprise determining if there was an engine operation at a predetermined high power level before the request for providing evaporated fuel was received during engine operation with non-hydrocarbon fuel, and providing evaporated fuel without switching to operation with hydrocarbon fuel when it is determined that there was an engine operation making the predetermined high power level.
According to this method, because there is a step of providing evaporated fuel without switching to operation with hydrocarbon fuel in the case that there was an engine operation making predetermined high power level during engine operation with non-hydrocarbon fuel, a time period from the generation of the evaporated fuel providing request to implement providing evaporated fuel can be shortened.
In another embodiment, the method may further comprise increasing engine output with non-hydrocarbon fuel for a predetermined period before switching fuel from non-hydrocarbon fuel to hydrocarbon fuel.
According to this embodiment, because the method has a step of increasing engine output with non-hydrocarbon fuel for a predetermined period before switching fuel from non-hydrocarbon fuel to hydrocarbon fuel, hydrocarbon purifying performance just after switching engine operation to use non-hydrocarbon fuel may be improved.
As one example of this embodiment, said dual-fuel engine has a battery charged by the engine and is provided in a hybrid system where a motor powers the vehicle and said dual-fuel engine is operated to generate electricity provided to the motor such that the engine may generate electricity by increasing engine output in the said step of increasing engine output with non-hydrocarbon fuel for a predetermined period. The method may further comprise a step of charging said battery via electricity generated by the engine.
According to this example, because the method has steps of generating electricity by increasing engine output and charging the battery using generated electricity, the method makes possible the simultaneous pursuit of inhibiting torque shock due to output increase and charging the battery in the hybrid system.
A second aspect of the present description includes a system for controlling a dual-fuel engine that is alternatively operable with non-hydrocarbon fuel or hydrocarbon fuel, the system comprising an evaporated gas providing device for providing an evaporated gas into said engine; a device for determining a cold engine operation; a fuel change device that causes a change in fuel type used in the engine depending on a driver's selecting operation; and a controller for controlling said evaporated gas providing device and fuel providing devices, wherein said controller is configured to: operate said engine with non-hydrocarbon fuel for a predetermined period irrespective of operation of said fuel change device when the cold engine operation is determined; determine that an evaporated fuel is to be provided into said engine; and switch to operation with hydrocarbon fuel and thereafter provide evaporated fuel into said engine when providing evaporated fuel into the engine is requested during engine operation with non-hydrocarbon fuel.
This system overcomes at least some of the disadvantages of above references in the same manner as the first aspect of the present description described above.
In one embodiment, said controller is further configured to determine that there was an engine operation making a predetermined high power level before a request was received to provide evaporated fuel during engine operation with non-hydrocarbon fuel, and provide evaporated fuel without switching to operation with hydrocarbon fuel when it is determined that there was an engine operation making the predetermined high power level.
According to this embodiment, because evaporated fuel is provided to the engine without switching to operation with hydrocarbon fuel in the case that there was an engine operation making the predetermined high power level during engine operation with non-hydrocarbon fuel, the time period from the generation of the evaporated fuel providing request to implementation of providing evaporated fuel can be shortened.
In another embodiment, said controller is further configured to increase engine output with non-hydrocarbon fuel for a predetermined period before switching fuel from non-hydrocarbon fuel to hydrocarbon fuel.
According to this embodiment, because the controller is further configured to increase engine output with non-hydrocarbon fuel for the predetermined period before switching fuel from non-hydrocarbon fuel to hydrocarbon fuel, hydrocarbon purifying performance just after switching engine operation to use non-hydrocarbon fuel may be improved.
As one example of this embodiment, said dual-fuel engine has a battery charged by said engine and is provided in a hybrid system where a motor powers a vehicle and said dual-fuel engine is operated to generate electricity provided to the motor such that said engine may generate electricity by increasing engine output when said controller increases engine output with non-hydrocarbon fuel for a predetermined period, wherein said controller is further configured to control said battery so that it charges via electricity generated by said engine.
According to this example, because the engine generates electricity by an increase in engine output and said battery is charged by generated electricity, the system makes possible the simultaneous pursuit of inhibiting torque shock due to output increase and battery charging in the hybrid system.
The above advantages and other advantages and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.